The present specification relates generally to the field of integrated circuits and to methods of manufacturing integrated circuits and the masks or reticles used to manufacture these devices. More particularly, the present specification relates to photon assisted deposition for hard mask formation on both device substrates and mask substrates.
Semiconductor devices or integrated circuits (ICs) can include millions of devices, such as, transistors. Ultra-large scale integrated (ULSI) circuits can include complementary metal oxide semiconductor (CMOS) field effect transistors (FET). Despite the ability of conventional systems and processes to put millions of devices on an IC, there is still a need to decrease the size of IC device features, and, thus, increase the number of devices on an IC.
One limitation to the smallness of IC critical dimensions is lithography. In general, projection lithography refers to processes for pattern transfer in various media on the substrate. It is a technique used for integrated circuit fabrication in which a silicon slice, the wafer, is coated uniformly with a radiation-sensitive film, the resist, and an exposing source (such as laser radiation, x-ray photons, or an electron beam) illuminates selected areas of the surface through an intervening master template, the mask, or reticle, for a particular pattern. The lithographic coating or photoresist is generally a radiation sensitive coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. The projected image may be formed using either negative or positive tone photoresist.
Exposure of the coating through a mask causes the image area to become selectively crosslinked where irradiated in the case of a negative tone photoresist and consequently less soluble in the developer fluid where the resist has been exposed. In the case of a positive tone resist, the exposed regions are rendered more soluble than the rest of the film due to deprotection of the polymers in the film where exposed to the imaging radiation. Subsequent to imaging using either tone of resist, the more soluble areas are removed in a developing process to leave the pattern image in the coating as the less soluble polymer. For both cases of resist types the difference in solubility is substantial so that a pattern with good fidelity is formed in the photoresist coating.
The pattern which results in photoresist from lithographic processing is used as a mask for the subsequent plasma etching of the underlying layer or layers. The plasma etch process directs chemical species to bombard the surface and remove material from the layer by means of chemical processes between species in the excited state in the plasma and the wafer surface. If the photoresist is durable enough for the etch warranted for the layer beneath, the resist mask enables transfer of the pattern to the underlying layer by means of the plasma etch process. If the resist mask by itself does not withstand the etch process necessary to etch the underlying layers an additional thin hard mask layer between the resist and the underlying layers to be patterned by the etch process is necessary. In that case, the resist mask is used with one type of etch process to etch the hard mask and a subsequent differing type of etch process to pattern the layers beneath. The final type of etch process does not attack the hard mask and is able to use the hard mask to prevent removal of the material in the desired areas as determined by the original pattern in the photoresist.
Projection lithography is a powerful and essential tool for microelectronics processing. As feature sizes are driven smaller and smaller, optical systems are approaching their limits due to the resolution capability of the combination of the wavelengths of optical radiation and photoresist in use by these systems.
Conventional lithography techniques often utilize a combination of photo-masks or reticles and hard masks to transfer patterns between various layers during integrated circuit fabrication. A hard mask is a layer of material on an integrated circuit wafer which prevents chemical removal of materials below the mask during plasma etch. A reticle is a patterning tool which contains patterns that can be transferred to an entire integrated circuit wafer in one or more exposures by means of a photoresist coating on the substrate being exposed.
Using a hard mask can increase the resolution capability of the manufacturing process by improving the plasma etch process capability by allowing a thinner resist coating to be used which will allow smaller dimensions to be produced in the resist and subsequently in the films comprising the semiconductor device on the wafer.
Another method of improving the device manufacturing capability is to improve the resolution capability of the reticle itself. Typically a reticle used in projection lithography has a 4xc3x97 or 5xc3x97 reduction factor so that reducing the minimum feature on the reticle substrate leads to a reduction in the size of the features at the wafer surface. The reticle substrate is coated with layers that are etched in an analagous method to the semiconductor device manufacture using a resist mask produced by exposure to radiation of some sort. Typically the layers are not made using a reticle or mask but rather are written by scanning the radiation from a database held in a computer.
There are several advanced techniques for forming reticles that allow more aggressive imaging resolution capabilities. These include phase shifting masks (PSMs) where the area surrounding the mask feature to be imaged are shifted in phase so as to interfere with the adjacent image from the pattern and create a smaller feature at the wafer surface. Here again, hard masks can be used to improve the manufacturing capability of reticles depending on the films used on the reticle substrates. For some types of phase shifting masks, the addition of the hard mask material itself can form the phase shifting region while for other types of PSMs the hard masks itself can be a layer which acts both as an etching hard mask and a film with optical properties enabling the phase shifting nature of that type of PSM.
Hard masks are generally created by depositing a material in blanket form by chemical vapor deposition (CVD). Subsequently, a pattern is etched from the hard mask layer using a photoresist mask and a variety of different etching or removal techniques. Due to the thickness of the resist and the response of the resist with the imaging system, the resolution capability of conventional systems is limited even with a hard mask. Thus, there is a need to use a photon assisted CVD type of deposition with either laser or synchroton radiation which allows direct patterning of hard mask layers without resist and allow for even greater resolution by selectively growing a thin layer of the hard mask at the sites irradiated by the photon.
Since there is a limitation to the resolution achievable with resist based pattern transfer with or without use of a hard mask to pattern the underlying layer, there is a need to pattern IC devices and reticles using non-conventional lithographic techniques. Furthermore, when patterning with hard masks, there is a need to use an alternative to forming a blanket of hard mask material over the surface of the integrated circuit wafer or the reticle since this must subsequently be etched with a resist based masking process. Yet further, there is a need for photon assisted deposition for hard mask formation due to the resolution enhancing capabilities of this non-resist based lithography since the layer can be selectively grown as a pattern for integrated circuit features.
An exemplary embodiment is related to a method of constructing an alternating phase-shifting mask. This method can include providing a vapor in a vapor chamber containing an integrated circuit substrate, and applying a laser to selected areas of the integrated circuit substrate to deposit material on the integrated circuit substrate. The material is configured to cause a 180xc2x0 phase shift.
Another exemplary embodiment is related to a system for forming an alternating phase-shifting mask. The system can include a vapor chamber, means for dispensing a chemical vapor in the vapor chamber, and means for providing radiation to a portion of an integrated circuit substrate to selectively deposit a material configured to cause a 180xc2x0 phase shift when the portion of the integrated circuit substrate is used as an alternating phase-shifting mask.
Another embodiment is related to a method of material deposition in the formation of an alternating phase-shifting mask. The method can include providing a chemical vapor in a vapor chamber containing an integrated circuit substrate, and selectively growing a material on the integrated circuit substrate by photon assisted chemical vapor deposition (CVD) until the material achieves a thickness to induce a 180 degree phase shift.